This application claims the benefit of Korean Patent Application No. 2001-40737, filed on Jul. 9, 2001 in Korea, which is hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a method of driving the liquid crystal display device.
2. Discussion of the Related Art
Liquid crystal display devices have been gaining in popularity in the display field because of their low power consumption and superior portability. Generally, the liquid crystal display device comprises a lower substrate, also referred to as an array substrate, an upper substrate, also referred to as a color filter substrate, and interposed liquid crystal between the upper substrate and the lower substrate. The lower substrate includes a thin film transistor. The upper substrate includes a color filter. Liquid crystal display devices use optical anisotropy and polarization properties of liquid crystals to display images. Presently, active matrix LCD (AM LCD) devices are one of the most popular means for displaying images because of their high resolution and superiority in displaying moving images. Accordingly, for purposes of discussion, all liquid crystal display devices hereinafter described refer to active matrix LCD (AM LCD) devices.
FIG. 1 illustrates a schematic view of a liquid crystal panel used in a conventional liquid crystal display device. As shown in FIG. 1, a liquid crystal panel 2 includes an upper substrate 4 having a common electrode (not shown), and a lower substrate 6 having a pixel electrode (not shown). A liquid crystal layer 8 is interposed between the upper substrate 4 and the lower substrate 6. A gate integrated circuit 10 and a data integrated circuit 12, used for applying a gate signal and a data signal, respectively, are positioned on the left and upper portion of the liquid crystal panel 2, respectively. A plurality of scanning lines gi, where xe2x80x9cixe2x80x9d is a positive integer and 1xe2x89xa6ixe2x89xa6n, are provided to receive a gate signal and a plurality of signal lines dj, where xe2x80x9cjxe2x80x9d is a positive integer and 1xe2x89xa6jxe2x89xa6m, are provided to receive a data signal on the lower substrate 6. The scanning lines and the signal lines cross each other to define a pixel region. A plurality of thin film transistors are formed at the crossing of the scanning lines and the signal lines. A liquid crystal capacitor CLC and a storage capacitor CST are connected in parallel to the thin film transistor.
A conventional driving method of the abovementioned liquid crystal display device will now be described with reference to FIGS. 2A-2C, 3A, 3B, and 4. Generally, the duration of time that the gate signal is applied to the scanning line such that the scanning line is in an xe2x80x9con-statexe2x80x9d is called a selection time. Conventional driving methods apply a higher voltage to the gate, which is connected to the scanning line, than a voltage applied to the signal line to reduce a resistance of a channel between a source electrode and a drain electrode during the selection time. Accordingly, the voltage applied to the signal line, also becomes applied to the liquid crystal layer through the pixel electrode. Conventional driving methods further apply lower voltage to the gate than a voltage applied to the signal line to electrically sever the source electrode and the drain electrode during a non-selection time. Accordingly, the electric charge accumulated in the liquid crystal layer during the selection time is maintained. By causing each scanning, line, from the first to the last, to undergo a selection time and a non-selection time, a frame of an image is made.
Referring to FIG. 2A, a timing chart illustrates a gate pulse applying method for each frame of a liquid crystal display device according to the related art. As shown in the FIG. 2A, all scanning lines of one frame are selected by applying an on-off gate pulse sequentially from the first scanning line g1 to the ith scanning line g1. For example, a first gate pulse 14a of a first frame and a second gate pulse 14b of a second frame are sequentially applied only once to pixels of the corresponding scanning line. After the first scanning line g1 undergoes the on-off of the gate pulse 14, the first scanning line g1 should maintain an alignment of the liquid crystal for one frame period until the gate pulse 14 is applied to the ith scanning line gi. This driving method is referred to as a hold type driving method.
Referring to FIG. 2B, another timing chart illustrates a method of processing image information for each frame in the hold type driving method. As shown in FIG. 2B, the hold type driving method maintains uniform image information for one frame. This processing method is possible only when a response speed of the liquid crystal equal to a speed of processing image information. However, twisted nematic (TN) liquid crystal, which is typically used in conventional liquid crystal display devices, has a response speed of 20 msec. The response speed of the liquid crystal within the liquid crystal display device, driven according to the hold type driving method, cannot catch up with the image information processing speed because a response speed of the liquid crystal suitable for motion picture must be at least under 5 msec. Accordingly, deterioration of displayed images occurs and results in a blurred motion of an image because the image information of the previous frame also remains in the next frame. Referring to FIG. 2B, the difference in height of the image information region for each frame indicates a gray level difference.
Referring to FIG. 2C, a chart illustrates a screen processing method of a hold type liquid crystal display device according to related art. As shown in FIG. 2C, at an arbitrary time, only image information on the selected scanning line 17 is refreshed. The selected scanning line 17 receives the image information of a new frame and, if the response speed of the liquid crystal cannot catch up with the image information processing speed, the image of the previous frame remains in the corresponding pixels of the selected scanning line 17 and thereby blurred motion results. Additionally, a data signal voltage, applied through the data integrated circuit, has a voltage different from a pixel voltage, applied to the pixel, due to resistance between lines in the course of arriving at the pixel or a parasitic capacitance in a portion of the thin film transistor. This voltage difference causes an image information difference between desired image information and actual image information. This image information difference brings about blurred motion in terms of visual perception.
Referring to FIG. 3A, a timing chart illustrates light emission profiles of a conventional cathode cay tube (CRT) display device. FIG. 3B illustrates a timing chart for a lighting operation curve of a conventional liquid crystal display device. In FIG. 3A, the light emission profile is individually formed for each frame by placing a black image section xe2x80x9cIxe2x80x9d, which makes a light intensity to become zero in a frame. As shown in FIG. 3B, because the liquid crystal display device uses a hold type driving method, and maintains fixed image form each frame, a continuous lighting operation curve is formed. An error region xe2x80x9cIIxe2x80x9d between the lighting operation curve and the data signal voltage brings about more blurred motion of an image as the frame is repeated. To overcome the above problem, a light emission profile according to two steps for each pixel is needed.
Referring to FIG. 4, a timing chart illustrates a related art method of processing image information for each frame in a liquid crystal display device using an impulsive type driving method. In the impulsive driving method, a certain portion of each frame is allocated a black image section xe2x80x9cIIIxe2x80x9d to prevent the image information of the previous frame from affecting the present frame. A double speed driving type liquid crystal display device, having a gate pulse with a short gate pulse width about xc2xd of the typical gate pulse width applied twice per frame using the impulsive driving method, has been suggested. However, because charging of the data signal voltage in the pixel is generally possible only when the gate signal voltage is in an xe2x80x9con-statexe2x80x9d, device properties within the thin film transistors within the liquid crystal devices need to be improved to increase the data processing speed. Accordingly, because a thin film transistor having a high field effect mobility is required to improve the device properties of the thin film transistor, choices for the semiconductor material is limited.
Accordingly, the present invention is directed a liquid crystal display device and a driving method for the liquid crystal display device that substantially obviates one or more of problems due to limitations and disadvantages of the related art.
An advantage of the present invention is to provide a liquid crystal display device that has a controller and a line memory to increase a data processing speed.
Another advantage of the present invention provides a driving method of the liquid crystal display device, in which an actual image and a black image are displayed alternately in a frame to prevent motion blur wherein a black image gate pulse and an actual image gate pulse are overlapped between two spaced scanning lines at an arbitrary moment of a frame to pre-charge a pixel voltage of pixels of the overlapped scanning line.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. Other advantages of the invention will be realized and attained by the stricture particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a liquid crystal display device comprises a liquid crystal panel including a plurality of scanning lines, a plurality of signal lines, a first substrate, a second substrate, and a liquid crystal layer interposed between the first substrate and the second substrate, wherein the scanning lines receive a gate signal, the signal lines receive a data signal and define a pixel region by crossing the scanning line, the first substrate includes a switching element that is connected to the scanning line and the signal line, the second substrate includes a common electrode, a gate integrated circuit and a data integrated circuit applies the gate signal and the data signal to the scanning line and the signal line, respectively, and a controller, wherein the controller outputs a gate start pulse for a reset image information and a gate start pulse for an actual image information to the gate integrated circuit at least once in a frame and controls a gate pulse for the reset image information and a gate pulse for the actual image information to be overlapped between two spaced scanning lines at an arbitrary moment. The liquid crystal display device further includes a line memory that stores the data signal of the controller and outputs the stored data signal to the data integrated circuit by dividing the data signal into at least two data signals and the controller outputs at least two data start pulses to each data integrated circuit, correspondingly, to a division method of the line memory. The line memory outputs the data signal to the data integrated circuit by dividing the data signal into three data signals. The liquid crystal is an optically compensated birefringence (OCB) mode liquid crystal that shows a bent structure when a voltage is applied. In one aspect of the invention, a normally white mode is adopted for the liquid crystal panel. The reset image information is black image information.
In another aspect, a driving method of a liquid crystal display device comprises the steps of applying a reset image data signal to corresponding pixels by sequentially applying a first gate pulse corresponding to a reset image information to each scanning line at a frame, and controlling the first gate pulse and a second gate pulse to be overlapped between two spaced scanning lines at an arbitrary moment in the first frame when the second gate pulse corresponding to an actual image information is sequentially applied to each scanning line with a certain time interval from the first gate pulse at the frame. The driving method of the liquid crystal display device further includes controlling a reset image data signal to be applied to an overlapped section of the first gate pulse and the second gate pulse, and controlling an actual image data signal to be successively applied to a non-overlapped section of the second gate pulse. A voltage that is applied to pixels of the overlapped section serves to pre-charge the successive actual image information. The reset image information is black image information. The first gate pulse precedes the second gate pulse. A reset image data and an actual image data, which are applied to the pixels to which the first gate pulse and the second gate pulse are applied, have a same polarity. A width of the first gate pulse has enough width to pre-charge the reset image data, and the reset image data is simultaneously applied to the scanning line to which the first gate pulse is applied and the scanning line to which the second gate pulse is applied in the overlapped section of the first gate pulse and the second gate pulse, and the actual image data is applied to the pixels of the scanning line to which the second gate pulse is applied in the section where only the second gate pulse is applied. The width of the first gate pulse and a width of the second gate pulse are different from each other. A size of a region in which the black image is displayed in a whole screen is controlled by a ratio between a first section that is from a start point of the first gate pulse to a start point of the second gate pulse in a frame and a second section that is from a start point of the second gate pulse in the frame to a start point of the first gate pulse in a next frame. A size of the first section and a size of the second section are different from each other. Both of the first section and the second section are longer than a response time of liquid crystal.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.